DE102006062157A1 - Birefringent and transparent optical media/probe retardation measuring and optical axis orientation position detecting method, involves aborting rotation of measuring system after reaching light intensity minimum, where system is measurable - Google Patents

Abstract

The method involves determining light intensity minimum by two wavelengths with a wedge compensator (7) in a first order along lines of an eyepiece under utilization of charge coupled device (CCD) rows (11, 12). Optical arrangement and length of retardation of an optical media or probe (5) are measured during existence of obliteration inclination by mechanical azimuthal rotation of a measuring system around an optical axis (1) of the system. The rotation of the system is automatically aborted after reaching the light intensity minimum, and the system is measurable. An independent claim is also included for a device for measuring high retardation of a birefringent and transparent optical media or probe and for detecting orientation position of an optical axis of the probe.

Description

The invention relates to a method and a device for the automatic, non-contact, high-speed and rapid measurement of high path differences R of birefringent and transparent optical media or samples and for simultaneous detection of the orientation position of the optical axis of these samples (cancellation obliquity) with a wedge compensator in the first order analog a Wright's eyepiece, multi-wavelength photoelectric scanning, and mechanical azimuthal rotation of this measuring system, particularly films and other fabrics, but also fibers and filaments, both in the laboratory, at the microscope, and online during the manufacturing process with rapid or slow changes (ms or seconds range). According to the method, all transparent films and other fabrics, but also fibers and filaments can be examined in the still molten state during manufacture or in the solid and stationary state. The measurement of the path difference R of the mentioned samples is important because it results in the birefringence with the aid of the thickness D of these samples Δn = R / D (1) which in many cases characterizes the orientation of the macromolecules in the films and fibers whose knowledge is important for fundamental investigations or technical interventions (proportionality to strength, inverse proportionality to elongation at break, uniformity of birefringence is proportional to color uniformity, etc.).

The birefringence Δn is in the case of the fibers always the difference of the refractive indices parallel and perpendicular to the fiber longitudinal axis, ie Δn = n || - n ⊥ , (2)

For the path difference R this applies analogously. In the case of optically uniaxial fibers of diameter D, the path difference R is the difference of the optical paths n _|| · D and n _⊥ · D, ie R = (n || - n ⊥ ) · D. (3)

In the first case (n _|| · D) the electric vector of the light oscillates perpendicular to the propagation direction, but parallel to the cylinder axis of the fiber. In the second case, he swings perpendicular to it.

is the path difference R is smaller than the used vacuum light wavelength λ, then called this area is the 1st order area (N + 1 = 1, ie N = 0). If the path difference between the wavelengths λ and 2λ, then this is the area of 2nd order (N + 1 = 2, so N = 1), etc. One speaks in general of the optical order (N + 1).

[State of the art]

For automatic and non-contact determination of the path difference in the area up to one wavelength, the Senarmont method is often used ( CH342768 . DE-AS 1097167 . DE 4123936 A1 . DE 4235065 A1 and DE 19529899 A1 ), which works with monochromatic light. For larger gait differences, this method is not suitable.

For gait differences greater than one wavelength λ, therefore, the Soleil-Babinet method is used ( DE 4123935 A1 and DE 4235065 A1 ), which works with white light. To DE 3 129 505 the measuring range is even limited to half a wavelength.

Multiple wavelength patents do not address the convergence of different orders at different wavelengths ( US 4,973,163 ). In US 5,406,371 Although the possibility of varying the wavelengths is present, but it is not simultaneously for the sizes referred to in the present patent as the measurement and auxiliary wavelength realized.

a A way out in the determination of the path difference in the presence of False colors offers the Senarmont method here, but applied with two wavelengths.

For path differences R> λ the minimum of the difference of the path differences of the two beams of different wavelengths is determined ( DE 4306050 A1 ). The disadvantage of this method, however, is that it is not fast enough because of the time-consuming determination of the minimum, ie there are no high sampling frequencies possible. In addition, the accuracy is limited because of the shallow maximum.

Height However, sampling frequencies are necessary to speed up the manufacturing process Shifting of special phenomena, eg. B. the shoulder (neck point) during rapid spinning or stretching process to capture.

In addition, will high sampling frequencies in the quality inspection required when z. B. a Monofilament is unwound from the spool and the orientation along the Thread to be determined at high take-off speed.

An elegant way to solve these problems is to use the Senarmont method having at least two wavelengths in very many angular positions of the analyzer ( DE 198 19 670 A1 ).

Becomes this latter method for measuring the path difference from shiny and for example, 15 microns thick fibers with the least light scattering used, then is the simultaneous (simultaneous) measurement of light intensities at least two wavelengths in very many angular positions (eg 10) of the analyzer very difficult because the scattered light also spreads to many recipients. This described method is therefore too faint and thus ultimately too inaccurate.

A newer patent ( DE 10 2004 051 247 ) describes a method in which the Senarmont method is carried out simultaneously or chronologically successively using the discrete Fourier analysis (DFA) with preferably three angular positions and at least two measuring wavelengths. In the case of the Senarmont method with simultaneous DFA, three angular positions are preferably simultaneously realized for scanning the signal coming from the object to be measured, and at least three optical cables with an upstream λ / 4 plate and three polarizers are required. With the Senarmont method with time-successive DFA, only one optical cable, one photoreceiver and one electrical amplifier are required. This increases the light intensity compared to the above-mentioned Senarmont process with very many angular positions of the analyzer.

adversely is in the mentioned methods for the determination of small path differences, that the orientation of the optical axis of the sample is not simultaneous can be determined because the mechanism is missing. But right now the optical axis is z. B. on the edge of slides both in their Production as well as during further processing not necessarily the withdrawal direction or other preferred directions in parallel (deletion skew). Without correction of the orientation of the measuring apparatus can already with angular deviations up to 5 ° error at the track difference of about 2% become effective.

at The method for determining large differences in gait must be in addition to Negation of extinction skew the linearity the photoreceptor be presupposed. It is not always given from the beginning.

Besides, they are for small samples and thin ones Threads the not bright enough. This concerns in particular the multi-color Senarmont method with discrete Fourier analysis, because here when operating with two wavelengths and three channels per wavelength the ones available for measurement Light intensity on six channels distributed.

OBJECT OF THE INVENTION

task The invention is the development of a method and a device for the automatic, non-contact, bright and fast measurement of high path differences R of birefringent and transparent optical media or samples and for simultaneous Detection of the orientation position of the optical axis of these samples (Extinction angle) being the linearity the photoreceptor must not be assumed, both in the laboratory, on the microscope as also on-line during the Manufacturing process with fast or slow changes (ms or seconds range).

According to the invention Task solved by that measurement with a wedge compensator in the first order analogous to a Wright's eyepiece, photoelectric scanning at several wavelengths and mechanical, azimuthal rotation of this measuring system is performed.

The Using the wedge compensator in conjunction with two wavelengths and photoelectric scanning by means of two CCD lines is z. B. with only two channels and therefore is also bright, fast and for the measurement suitable for high gait differences. By the rotation of the measuring system is in complicated cases the measurement at all only possible and the orientation of the optical axis of the sample (the extinction slant) can be specified.

The Method can be used for automatic, non-contact, high-speed and rapid measurement of the path difference of double refracting samples even if the position of the optical axis of the sample changes. The Execution of the The method is explained by the following examples.

[Examples]

1. Scheme of the procedure

1.1 Large differences in gait

In 1 the scheme of the method is shown, according to which the radiation of the light source ( 2 ) via the condenser ( 3 ) and the polarizer ( 4 ) to the test ( 5 ) with the lens ( 6 ) is displayed in the intermediate image plane. For measuring the path difference at the measuring wavelength λ ₁ , a wedge compensator ( 7 ) (in the first order) analogous to a Wright's eyepiece used. Behind the compensator ( 7 ) is the analyzer ( 8th ). By using the two filters ( 9 ) and ( 10 ) guarantees a two-wavelength measuring method, where λ _{1 is} the measuring wavelength and λ _{2 is} the auxiliary wavelength.

The CCD lines are used to track the intensity of the light along the wedge compensator, separated for the measuring wavelength ( 11 ) and for the auxiliary wavelength ( 12 ). After amplifying the radiation intensities with the amplifiers ( 13 ) and ( 14 ) is connected to the PC ( 15 ) determines the respective minimum intensity for the radiation of the measuring wavelength λ ₁ and the auxiliary wavelength λ ₂ . Due to the known assignment of the location of the intensity minimum and the path difference R in the wedge compensator ( 7 ), the _path differences R _λ1 (1) and R _λ2 (1) can be given in the first order. The PC calculates the absolute and rounded size N = {R _λ2 (1) - R _λ1 (1)} / {λ ₁ - λ _2}, which results in the retardation R _λ1 for the measuring wavelength λ ₁ to R _λ1 = R _λ1 (1) + N · λ ₁ yields.

• – zum Aufsuchen des Intensitätsminimums I_λ1 und Bestimmung der Zuordnung des Ortes L und des Gangunterschiedes R_λ1(1) in der ersten Ordnung für die Mess-Wellenlänge;
• – zum Aufsuchen des Intensitätsminimums I_λ2 und Bestimmung der Zuordnung des Ortes L und des Gangunterschiedes R_λ2(1) in der ersten Ordnung für die Hilfs-Wellenlänge;
• – zum Berechnen der absoluten und gerundeten Größe N = {R_λ2(1) – R_λ1(1)}/{λ₁ – λ₂} und schließlich
• – zum Berechnen des gesuchten Gangunterschiedes für die Wellenlänge λ₁ Rλ1 = Rλ1(1) + N·λ1.

The PC is used

• - To search the intensity _minimum I _λ1 and determining the assignment of the location L and the _path difference R _λ1 (1) in the first order for the measuring wavelength;
• - To search the intensity _minimum I _λ2 and determining the assignment of the location L and the _path difference R _λ2 (1) in the first order for the auxiliary wavelength;
• - for calculating the absolute and rounded size N = {R _λ2 (1) - R _λ1 (1)} / {λ ₁ - λ _2}, and finally
• - To calculate the sought path difference for the wavelength λ ₁ R λ1 = R λ1 (1) + N · λ 1 ,

The mechanical axis, which lies in the optical axis of the measuring system, is coupled to a stepper motor, which can rotate the entire measuring system azimuthally through the angle α. The stepper motor is rotated until the minimum of the intensity of the radiation of wavelength λ ₁ (I _λ1 ) is reached. Then the wedge compensator is perpendicular to the sample. The calculation of the desired _path difference R _λ1 can begin. For perfect measurement, the sample and the wedge compensator as well as the polarizer and the analyzer must each be perpendicular to each other, as shown in 2 is shown.

The mutual assignment of thickness D of the wedge compensator ( 7 ) and path difference R is in the first field of 3 shown. The black bar should indicate the light intensity minimum.

In the same 3 underneath is the wedge compensator ( 7 ) assigned position of the CCD line ( 11 ), in which the wedge compensator ( 7 ) documented light intensity minimum at location L of this line.

1.2 extinction skew

If the orientation of the optical axis of the sample changes as a result of changed technological conditions, ie if it is skewed to an excellent preferred direction (extinction slant), then it rotates azimuthally through the angle α1, see 4 , As a result, the light intensity changes, which then triggers a signal for the azimuthal rotation of the measuring system with the stepper motor. This rotation of the measuring system by the angle α2 takes place until the light minimum is reached again. Then, at the same time, α1 = α2. The new measurement can begin.

2. Method for a 1-1 / 4-λ plate

For a 1-1 / 4-λ plate, the first-order path difference was found with the wedge compensator ( 7 ) at the measuring wavelength
589.3 nm to R _λ1 (1) = 84.7 nm.

At the auxiliary wavelength resulted with the wedge compensator ( 7 ) For
656.3 nm, the _path difference in the first order to R _λ2 (1) = 24.2 nm.

from that the absolute and rounded N value follows N = (24,2-84,7) / (589,3-656,3) = 0.903 ≈ 1.

This makes it possible to increase the path difference for the 1-1 / 4-λ plate at the measurement wavelength of 589.3 nm with N = 1 R λ1 = 84.7 + 1 × 589.3 = 674 nm to calculate.

With the Ehringhaus compensator was determined comparatively 677 nm, d. H. a good match the results.

3. extinction slant with a λ-plate

At the measurement wavelength of 589.3 nm, the following increase in intensity resulted for a λ-platelet with rotation through the angle α after a previous minimum position: angle α light intensity in SKT 0 ° 7 10 ° 180 20 ° 618 ° 30 1090 40 ° > 1200

By the azimuthal Nachdrehung of Measuring system around the optical axis of this system, the perfect measurement of the path difference was possible in all angular positions.

4th variant of the embodiment 1.1

In 5 the scheme of a variant of the method is shown, according to which the radiation of the measuring and the auxiliary wavelength (λ ₁ and λ ₂ ) from the outset by two laser diodes ( 19 ) and ( 20 ) will be realized. Both radiations are alternatively excited, so that the measuring and then the auxiliary wavelength are available in a short time interval. The auxiliary wavelength is transmitted through the prism ( 21 ) directed into the main beam path. The prism is there for the straight passage of the radiation of the measuring wavelength λ ₁ and for the 90 ° deflection for the auxiliary wavelength λ ₂ . Measuring and auxiliary wavelength are separated in time via the condenser ( 3 ) and the polarizer ( 4 ) to the test ( 5 ), with the lens ( 6 ) is displayed in the intermediate image plane. For measuring the path difference at the measuring wavelength λ ₁ and at the auxiliary wavelength λ ₂ , a wedge compensator ( 7 ) (in the first order) analogous to a Wright's eyepiece used. Behind the compensator ( 7 ) is the analyzer ( 8th ). With the CCD line ( 22 ) the intensity of the light is tracked along the wedge compensator, separated in time for the measuring wavelength ( 19 ) and for the auxiliary wavelength ( 20 ). After amplifying the radiation intensities with the amplifier ( 23 ) is connected to the PC ( 15 ) determines the respective minimum intensity for the radiation of the measuring wavelength λ ₁ and the auxiliary wavelength λ ₂ . Due to the known assignment of the location of the intensity minimum and the path difference R in the wedge compensator ( 7 ), the _path differences R _λ1 (1) and R _λ2 (1) can be given in the first order. The PC calculates the absolute and rounded size N = {R _λ2 (1) - R _λ1 (1)} / {λ ₁ - λ _2}, which results in the retardation R _λ1 for the measuring wavelength λ ₁ to R _λ1 = R _λ1 (1) + N · λ ₁ yields.

5th variant of the embodiments 1.1 and 4

If a thread or a ribbon is used as a sample, then the ray path must be bent as in the Senarmont method or when using the Soleil-Babinet method ( Sz-PS-342768 . DE-AS 1097167 . DE 4123936 A1 . DE 4235065 A1 . DE 19529899 A1 . DE 4123935 A1 and DE 4235065 A1 ).

6. Device for measuring large path differences

In 1 the scheme and the arrangement of the device is shown, in which all optical elements along the optical axis ( 1 ) are arranged. On the light source ( 2 ) and the condenser ( 3 ) follow the polarizer ( 4 ) and the lens ( 6 ). Between polarizer ( 4 ) and lens ( 6 ) is the measured, running or static slide ( 5 ). To the lens ( 6 ), which takes over the image in the intermediate image plane, the wedge compensator closes ( 7 ), after which the analyzer ( 8th ) is arranged. Analyzer ( 8th ) and polarizer ( 4 ) are crossed, ie their polarization directions are perpendicular to each other, as in (2) is shown. Polarizer ( 4 ) and analyzer ( 8th ) are therefore connected to a stepper motor. Above the analyzer ( 8th ) there are two filters ( 9 ) and ( 10 ), which serve to separate the measuring wavelength and the auxiliary wavelength. The following CCD lines ( 11 ) and ( 12 ) are arranged so that they can take over the electronic scanning of the position of the located on the wedge compensator interference fringe whose fundamental position in (3) is specified. After that, the amplifiers ( 13 ) and ( 14 ), so that the computer ( 15 ) can ultimately calculate the optical order (N + 1) and the sought path difference R.

7. Device for determining the deletion skew

The in 1 Positioned at the third position polarizer ( 4 ) and the analyzer located at the seventh position ( 8th ) are about the optical axis ( 1 rotatably mounted, wherein the rotation itself takes place via the stepper motors connected to them. Exactly this is basically important for the process, so that polarizer ( 4 ) and analyzer ( 8th ) are perpendicular to each other ( (2) ) and so that they are in a 45 ° position to the again mutually perpendicular elements foil ( 5 ) and wedge compensator ( 7 ) can be located ( (2) ).

Only in this way is it possible that in a renewed position of the device both the analyzer ( 8th ) as well as the polarizer ( 4 ) until, due to the changed position of the molecular axes in the film ( 5 ) the previous light minimum is reached again.

Prerequisite is the coupling of the stepper motors with the computer ( 15 ).

• – zum Aufsuchen des Intensitätsminimums I_λ1 und Bestimmung der Zuordnung des Ortes L und des Gangunterschiedes R_λ1(1) in der ersten Ordnung für die Mess-Wellenlänge;
• – zum Aufsuchen des Intensitätsminimums I_λ2 und Bestimmung der Zuordnung des Ortes L und des Gangunterschiedes R_λ2(1) in der ersten Ordnung für die Hilfs-Wellenlänge;
• – zum Berechnen der absoluten und gerundeten Größe N = {R_λ2(1) – R_λ1(1)}/{λ₁ – λ₂} und schließlich
• – zum Berechnen des gesuchten Gangunterschiedes für die Wellenlänge λ₁ Rλ1 = Rλ1(1) + N·λ1.

The PC is used

• - To search the intensity _minimum I _λ1 and determining the assignment of the location L and the _path difference R _λ1 (1) in the first order for the measuring wavelength;
• - To search the intensity _minimum I _λ2 and determining the assignment of the location L and the _path difference R _λ2 (1) in the first order for the auxiliary wavelength;
• - for calculating the absolute and rounded size N = {R _λ2 (1) - R _λ1 (1)} / {λ ₁ - λ _2}, and finally
• - to calculate the searched passage difference for the wavelength λ ₁ R λ1 = R λ1 (1) + N · λ 1 ,

The mechanical axis, which lies in the optical axis of the measuring system, is coupled to a stepper motor, which can rotate the entire measuring system azimuthally through the angle α. The stepper motor is rotated until the minimum of the intensity of the radiation of wavelength λ ₁ (I _λ1 ) is reached. Then the wedge compensator is perpendicular to the sample. The calculation of the sought _path difference R _λ1 can begin

1

optical Axis of the measuring system

2

White light source with pass filter for the wavelengths λ ₁ and λ ₂

3

condenser

4

polarizer

5

sample (Foil or other birefringent sample [sheets])

6

Lens for the intermediate image of the sample 5

7

Keilkompensator for the first order in the intermediate image plane

8th

analyzer

9

Filter for the radiation of wavelength λ ₁ (measuring wavelength)

10

Filter for the radiation of wavelength λ ₂ (auxiliary wavelength)

11

CCD line for the wavelength λ ₁

12

CCD line for the wavelength λ ₂

13

Amplification for the radiation of the wavelength λ ₁ (I _λ1 ) for all sections L of the CCD line ( 11 ) from L0 to Lmax

14

Amplification for the radiation of wavelength λ ₂ (I _λ2 ) for all sections L of the CCD line ( 12 ) from L0 to Lmax

15

PC

16

mechanical axis

17

α1 = extinction skew the sample (oblique orientation of the optical axis)

18

α2 = Azimuthal rotation of the measuring system up to the intensity minimum (see 13 and 15 ).

19

Diode laser for the measuring wavelength λ ₁

20

Diode laser for the auxiliary wavelength λ ₂

21

prism

22

CCD line for scanning the radiation of the wavelengths λ ₁ or λ ₂

23

Amplification for the radiation of the wavelengths λ ₁ (I _λ1 ) or λ ₂ (I _λ2 ) for all sections of the CCD line ( 22 ) from L0 to Lmax (corresponds to the effect of ( 12 ))

Claims (7)

Method for the automatic, non-contact, fast and fast measurement of high path differences R of birefringent and transparent optical media or samples and for the simultaneous detection of the orientation position of the optical axis of these samples (cancellation obliquity), wherein the linearity of the photoreceivers is not assumed, characterized in that determined at least two wavelengths with a wedge compensator in the first order analogous to a Wright's eyepiece with the aid of a CCD line, the light intensity minimum, from the optical order and finally the path difference R are calculated, even in the presence of a deletion skew by mechanical, azimuthal rotation of the measuring system about the optical axis of the measuring system is possible in that the rotational movement is automatically stopped after reaching the light intensity minimum and the system is able to measure again. Method according to Claim 1 for exactly two wavelengths, characterized in that the path differences R _λ1 (1) and R _λ2 (λ ₎ determined at the wavelengths λ ₁ (measuring wavelength) and λ ₂ (auxiliary wavelength) with the wedge compensator in the first order 1) N = {R _λ2 (1) - R _λ1 (1)} to an absolute number and rounded / {λ ₁ - λ _2} further processed and the path difference for the measuring wavelength to R λ1 = R λ1 (1) + N · λ 1 , is calculated, this method is still valid when the sample rotates azimuthally by the angle α, because then the light intensity in the light intensity minimum decreases, which has an azimuthal rotation of this measuring system also up to the azimuthal angle α result so that the correct measurement can be made. Method according to Claims 1 and 2, characterized that for Fibers, filaments and thread ribbons the beam path must be angled. Device for realizing the method for the automatic, non-contact, fast and fast measurement of high path differences R of birefringent and transparent optical media or samples and for the simultaneous detection of the orientation position of the optical axis of these samples (extinction slant), whereby the linearity of the photoreceivers is not assumed characterized in that all the optical elements along the optical axis ( 1 ) are arranged on the light source ( 2 ) and the condenser ( 3 ) follow the polarizer ( 4 ) and the lens ( 6 ), between polarizer ( 4 ) and lens ( 6 ) is the measured, running or static slide ( 5 ), to the lens ( 6 ), the wedge compensator closes ( 7 ), after which the analyzer ( 8th ), analyzer ( 8th ) and Polarisa gate ( 4 ) are crossed and connected to a stepper motor, above the analyzer ( 8th ) there are two filters ( 9 ) and ( 10 ) for separating the measuring wavelength and the auxiliary wavelength, the following CCD lines ( 11 ) and ( 12 ) are arranged so that they can take over the electronic scanning of the position of the located on the wedge compensator interference stiffness, then the amplifier ( 13 ) and ( 14 ), so that the computer ( 15 ) can ultimately calculate the optical order (N + 1) and the sought path difference R. Device according to claim 4, characterized in that the polarizer ( 4 ) and the analyzer ( 8th ) about the optical axis ( 1 ) are rotatably mounted, wherein the rotation itself takes place via the stepper motors connected to them. Apparatus according to claim 5, characterized in that polarizer ( 4 ) and analyzer ( 8th ) are perpendicular to each other and in 45 ° position to the again mutually perpendicular to each other elements foil ( 5 ) and wedge compensator ( 7 ) are located. Apparatus according to claim 5, characterized in that the stepper motors with the computer ( 15 ) are coupled.